The lipid fluidity (reciprocal of misroviscosity-.eta.) of biological membranes is determined by their structure and chemical composition and, in particular, the mole ratio of cholesterol to phospholipids (C/PL), the mole ratio of sphingomyelin to lecithin (S/L) and the degree of unsaturation of the phospholipid acyl chains (Shinitzky and Henkart, Int.Rev.Cytol. 60, 121 (1979); Cooper, J., Supramol.Struct. 8, 413 (1978)).
The membrane lipid fluidity, in turn determines many of the physiological properties of receptors (Muller and Shinitzky, Brit.J.Haematol. 42, 355 (1979); Heron, et al., Proc.Natl.Acad.Sci. USA, 77, 7463 (1980); Heron et al., in "Receptors and their Neurotransmitters", eds. Littauer et al., John Wiley, London (1980); Heron et al., Eur.J.Pharmacol. 72, 361 (1981), antigens (Shinitzky and Souroujon, Proc.Natl.Acad.Sci. USA 76, 4438 (1979) enzymes (Sandermann, Biochim.Biophys.Acta, 515, 209 (1978); Rimon et al., Nature, 270, 267 (1977), transport carriers (Kimelberg, Biochim.Biophys.Acta, 413, (1975), ion channels (Stephens and Shinitzky, Nature, 270, 267 (1977), and ribosomes (Towers et al., Biochim.Biophys.Acta, 287, 301 (1972) which are bound to these membranes in the brain and other organs. This subject was recently extensively reviewed (Shinitzky, Physiol. Rev. in press).
The final response of target cells depends, therefore, on the structural and dynamic properties of their membranes, which are determined by their lipid composition. One may, therefore, expect an optimal lipid fluidity for the maximal response of each target cell (Heron et al., Proc.Natl.Acad.Sci. USA, 77, 7463 (1980); Heron et al., in "Receptors and their Neurotransmitters", eds. Littauer et al., John Wiley, London (1980); Yuli et al., Biochemistry, 20, 4250, (1980); Shinitzky, Physiol. Rev., in press).
In many disorders, the pathogenesis involves changes in membrane lipid composition or lipid metabolism (Cooper, N.Engl.J.Med., 297, 371 (1977)). These changes have been correlated in many cases to an increase in membrane lipid miscroviscosity of various tissues due to an increase in C/PL or S/L or a decrease in the degree of unsaturation of the phospholipid acyl chains or any combination of the three. Lipid peroxidation can also affect the dynamics of cell membrane proteins and consequently the overt physiological functions (Sagai and Ichinose, Life Sci., 27, 731 (1980)). The following is a list of such disorders mediated by lipid imbalances, all of which are amenable to lipid manipulations:
(1) Aging and senescence (Yamamoto, Lipids, 3, 284 (1968); Rivnay et al., Mech. Age. Dev. 10, 71 (1979); Heron et al., to be published; see also Table 4 in this specification; Araki and Rifkind, Life Sci. 26, 2223 (1980); Hershkowitz et al., Progress in Brain Research, Elsevier-North Holland, in press); Rouser et al., Avd. Lipid Res. 10, 262 (1972).
(2) Withdrawal symptoms of drug and alcohol addiction (Johnson et al., Mol.Pharmacol., 15, 739 (1979); Chin and Goldstein, Science, 196, 684 (1979); Littleton and John, J.Pharm.Pharmac., 29, 579 (1977); Heron et al., Biochem,Pharmacol. in press (1982); see also Table 3 in this specification).
(3) Hyperlipidemic disorders such as hypertension, atherosclerosis, gallstones, cirrhosis, and obesity (Montenay et al., Biochem.Biophy.Res.Comm. 100, 660 (1981); Cooper, N., Engl.J.Med., 297, 371 (1977); Miettinen et al., Lancet 2, 835 (1972).
(4) Sperm infertility (Davis et al., Biochim.Biophys. Acta, 558, 257 (1979); Davis, Proc.Soc.Exp.Biol.Med., 152, 257 (1976)).
(5) Impaired immune function such as in aging, obesity and certain cases of allergies (Rivnay et al., Mech.Age.Dev., 12, 119 (1980); Rivnay et al., Mech.Age.Dev. 10, 71 (1979).
We have also shown that synaptic membrane miscroviscosity increases as a result of surgical or chemical lesions of specific pathways in the brain (Heron et al., Biochem.Pharmacol., in press (1982). These findings may apply to other degenerative or organic damages such as Alzheimer's disease, Parkinsonism, Tardive dyskinesia, Huntington's chorea, tremor, ataxia, and epilepsy and certain cases of mental retardation, all of which could in principle be treated by lipid manipulation.
It is also generally accepted that certain mental disorders such as mania, depression and schizophrenia are related to a chemical imbalance in the turnover rate of neutrotransmitters in the brain. There is evidence to suggest that the biogenic amines (dopamine, norephinephrine and serotonin) are primarily involved. The receptors and membranes bound enzymes concerned with turnover of these transmitters can be altered by changes in membrane fluidity (Hershkowitz et al., Progress in Brain Research, Elsevier-North Holland, in press; Heron et al., Proc.Natl.Acad.Sci. USA 77, 7463 (1980); Heron et al., in "Receptors and Their Neurotransmitters", eds. Littauer et al., John Wiley, London (1980); Heron et al., Eur. J.Pharmacol., 72, 361 (1981), and therefore also falls into the category of disorders amenable to lipid manipulations.
Modulation of function by lipid manipulations can also be carried out in vitro. This could be applicable to modulation of viral infectivity for use in vaccinations (Pal et al., Biochemistry 20, 530 (1981), and antigenicity (Shinitzky and Souroujon, Proc. Natl.Acad.Sci., USA 76, 4438 (1979)), which could reduce tissue rejection and facilitate transplatations.
We have found that some of the adverse effects mediated by lipid imbalances could be rectified by a form of "membrane engineering", through the use of an active fraction of lipids from natural sources. This fraction (which contains a substantial portion of lecithin) can operate via several possible mechanisms:
(1) Extraction of excess cholesterol by passive translocation (Cooper, J.Supramol.Struct., 8, 413 (1978); Miettinin et al., Lancet, 2, 835 (1972); Morison, Geriatrics 13, 12 (1958); Cooper et al., J.Clin.Invest. 55, 115 (1975)). PA0 (2) Exchange with membrane lipids of higher microviscosity (Wirtz and Zilversmit, Biochim.Biophys. Acta 193, 105 (1969). PA0 (3) Net incorporation into or replacement of damaged lipids (e.g. peroxidized) (Bakardjieva et al., Biochemistry 18, 3016 (1979)). This could restore the structure and function of degenerate membranes. PA0 (4) Precursors in various metabolic pathways (e.g. prostaglandins, vitamin D and acetylcholine). PA0 (1) Fluidization is effected by a well defined portion of the lipids, while the rest serve as essential carriers which facilitate transport and absorption into the membranes. PA0 (2) The assembly of the active and the carrier components is of defined physico-chemical characteristics, such as the surface density and charge distribution. PA0 (3) These characteristics could be optimal for proper transportation, associated with cell surfaces, disintegration, unloading or exchange, as dictated by the site of interaction. PA0 (4) The various lipid components could act synergistically to effect the activities described above. PA0 (5) The degree of unsaturation is optimal, i.e. it has the necessary fluidity characteristics (the transition from fully saturated to mono-unsaturated is the most critical to fluidizing ability, while the transition from mono to poly-unsaturated does not significantly change the fluidizing ability (Hubbel and McConnell, J.Am.Chem.Soc. 93, 314 (1971); Stubbs et al., Biochemistry 20, 4257 (1981)), and yet not too unsaturated, thus less vulnerable to oxidation. PA0 1. Increased vulnerability to bacterial contaminations; PA0 2. Dysfunctions of the immune system; PA0 3. Allergies; PA0 4. Hypertension; PA0 5. Hyperlipidemic states such as atherosclerosis, gallstones, cirrhosis and obesity, and the like; PA0 6. Symptoms of withdrawal from alcohol and other drugs; PA0 7. Prevention of tolerance to drugs. PA0 (1) The lipid extract from egg yolk (e.g. crude lecithin) is dissolved in chloroform, evaporated to almost dryness, acetone is added to effect a precipitation of a certain part of the lipid, and the supernatant is removed, evaporated and the solvent is removed to complete dryness, leaving a fraction of about 5 weight percent of the initial quantity of the untreated egg-yolk, which is the desired fraction AL. An antioxidant such as tocopherol is added to a final concentration of about 0.5% (w/w). Analysis of the lipid composition of this fraction (Preparation 1) is given in Table 1. PA0 (2) A natural lipid source (e.g. egg yolk, soybean) is first mixed with acetone to remove excess undesired lipids. The precipitate is then treated again with acetone, and the supernatant is collected, evaporated to complete dryness, leaving a fraction of about 10-15 weight percent of the initial quantity of the untreated egg-yolk, which is the desired fraction AL. An antioxidant such as tocopherol is added to a final concentration of about 0.5% (w/w). Analysis of the lipid composition of this fraction (Preparation 2) is also given in Table 1. Amongst other solvents which can be used there may be mentioned: chloroform-methanol 1:1 v/v, hexane, tetrahydrofuran, acetonitrile, ethanol, methanol, diethyl ether and diethyl ketone. PA0 (3) A natural lipid source (e.g. egg-yolk, soybean) is first mixed with acetone to remove excess undesired lipids. The precipitate is then treated again with acetone, and the supernatant is collected and cooled below 0.degree. C., upon which the desired fraction (AL) amounting to about 10-15 weight percent of the initial quantity of the untreated egg-yolk, is precipitated and collected. An antioxidant such as tocopherol is added to a final concentration of about 0.5% (w/w). Analysis of the lipid composition of this fraction (preparation 3) is given in Table 1 and 2. Amongst other solvents which can be used there may be mentioned: chloroform-methanol 1:1 v/v, hexane, tetrahydrofuran, acetonitrile, ethanol, methanol, diethyl ether and diethyl ketone.
However, diets having a high content of lecithin, which are frequently recommended for a variety of disorders (Cobb et al., Nutr.Metab., 24, 288 (1980); Blass (Cornall-Burke Rehabilitation Center); Gershon (Lafayette Clinic, Detroit); Heyman (Duke University Med. Center); Sullivan et al., (M.I.T. and Tufts Univ.), in "Proceedings of the International Study Group on the Pharmacology of Memory Disorders Associated with Aging", Zurich (1981)), are not very effective in alleviating symptoms associated with lipid imbalances and in restoring membrane lipid fluidity to normal. The reasons for this are not yet clear. It seems that the previously proposed rationale for these lecithin treatements, which are based either on its acetycholine precursor role or on the high degree of unsaturation covers only a minor aspect of this approach (Herring et al., Biochim.Biophys.Acta 602, 1 (1980); Shinitzky and Henkart, Int. Rev. Cytol. 60, 121 (1979)).
It is plausible that the process of lipid manipulation combines several prerequisites such as the following: